The present invention relates to an optical switching device for providing a signal switching function for use in a wavelength-multiplexing optical communication, in particular, to an optical switching device for use in, for example, an optical communication path for a LAN, an optical bus for a computer system, a connection bus for various electronic units, and an in-rack optical signal wiring.
In most conventional optical communication systems, wavelengths of 1.3 .mu.m-band or 1.5 .mu.m-band have been used. In recent years, however, to construct large capacity optical communication systems using wavelength-multiplexing, a technique for inserting a large number of wavelengths of signals at intervals of several nano-meters based on such two bands is being studied. When this technique is established, an optical communication system with a very narrow band can have a large capacity. The communication switching technique which deals with such a narrow band is, however, just in an initial stage of study. Thus far, such a technique has not been accomplished.
To accomplish a switching function of such a wavelength-multiplexing optical communication system, a technique for mixing and dividing a large number of optical signals with different wavelengths is essentially required. With conventional optical filters, it is difficult to satisfactorily obtain desired signal levels and S/N ratios. In particular, when a large number of signals with different wavelengths in a narrow band are used, S/N ratios of the signals are remarkably degraded. With a number of filters connected, the S/N ratios may be improved. However, the signal levels are remarkably lowered due to signal losses. Thus, with the conventional technique, a desired switching function cannot be accomplished.
To accomplish such a switching function, a semiconductor device named a tunable filter which filters a signal on the order of several nm is being developed. However, it will take a long time to complete such a device. In addition, since such an active device requires synchronization of wavelengths, thereby confronting large technical difficulties (as in Minoru AKIYAMA et. al. "Photonic Switching System" IEICE Transactions VOL E74, No. 1, January 1991).